Siloxane resins are known to be materials of high heat resistance, of high hardness, of high insulation and of high transparency, and hence are used for various applications. As one of those applications, a siloxane resin-containing composition is cured to form a hardened coating, which has high durability, low dielectricity, high insulativity and high hardness. By making good use of those properties, the hardened coating is employed as an insulating film, a planarization film or a protective film in a semiconductor device or in a liquid crystal display. Further, it can be also adopted as a semiconductor sealant.
Siloxane resins are produced by hydrolysis of alkoxysilane or halosilane compounds, and hence contain silanol groups therein. The silanol groups contribute to alkali-solubility, and this property of silanol groups is made good use of in various reported photosensitive siloxane resin compositions that can be developed with a developer normally adopted in the field of electronic materials, in particular, with a 2.38% aqueous solution of tetramethylammonium (Patent document 1).
For the purpose of alkali-solubilizing a siloxane resin, it is generally thought to increase the content of silanol groups, namely, to reduce the molecular weight of the resin. However, if the molecular weight is reduced, the resin tends to deteriorate in resistance to thermal reflow processing. Specifically, when the composition is cured to form a film at 200° C. or more, pattern collapse is liable to occur. On the other hand, however, if the resin has too large a molecular weight, the sensitivity can be so lowered that it takes long time to perform exposure and/or development. Further, it is also feared that residues (hereinafter, often referred to as “scum”) can be left after development in the area where the composition must be dissolved away with a developer.
In order to improve the resistance to thermal reflow processing while keeping the alkali-solubility, it is studied to use a siloxane resin having a molecular weight low enough to be alkali-soluble in combination with a high molecular weight alkali-insoluble resin. The more those two resins have different molecular weights, the more the resistance to thermal reflow processing is enhanced (Patent document 2). However, the present inventors have found that there still remains a problem of increasing scum remarkably. There are also other proposed methods, such as, addition of a hardening agent (Patent document 3) and incorporation of silica (SiO2) units into the resin (Patent document 4), but they also have room for improvement. Specifically, the method of Patent document 3 tends to increase scum, to lower the temporal stability and to impair the sensitivity. Further, if the polymer contains the silica units in an amount of more than 30 mol %, the method of Patent document 4 tends to increase scum and to lower the temporal stability remarkably.
As a means for solving the above problems, it is often to use multifunctional polysiloxane having neither alkoxy groups nor hydroxyl groups. However, this polysiloxane has disadvantageous properties, such as, low hardenability and poor transparency (Patent document 5).